1. Field of the Invention
This invention relates to a color separation optical system for a color television camera, and more particularly to an improvement of a color separation optical system provided with a bias light device.
2. Description of the Prior Art
Generally, in the color separation optical system for a color television camera, a bias light system should be provided to illuminate the light receiving face of an image pick up element such as an image pick up tube or CCD (charge coupled device) for improving various properties thereof such as rise characteristics and after image characteristics. Since the bias light should normally be provided simultaneously on the light receiving faces of image pick up elements for three primary color channels R.G.B., the bias light is usually guided into a color separation optical system so that the bias light may be provided on the three color channels through the color separation optical system. Such a system is advantageous in that only one light source is needed for the bias light and the structure of the system including the light source is made simple. Japanese Patent Publication Nos. 29888/1975 and 29889/1975 show such examples.
Recently, there has been made a trial to improve the sensitivity of the camera by 18 dB in an electric system in order to obtain color images in comparatively dark scenes. Under such circumstances, the above mentioned bias light system is insufficient because of ununiform distribution of bias light illumination.